1. Field of the Invention:
The present invention relates to an improved process for preparing polyisocyanurate/polyisocyanates via the partial catalytic cyclotrimerization of polyisocyanates, with the reaction being subsequently stopped at will when the trimer content thereof reaches the desired or predetermined value. More particularly, the present invention relates to an improved technique for deactivating the catalyst employed in the aforesaid process, when the catalyst comprises a compound which includes an aminosilyl function.
2. Description of the Prior Art:
In French Pat. No. 82/03799, published under No. 2,522,667 and published European Patent Application No. 0,089,297 (U.S. Pat. No. 4,537,961), a process is described for preparing polyisocyanurate/polyisocyanates by catalytic cyclotrimerization of polyisocyanates, using catalyst compounds containing aminosilyl groups, according to which, when the desired content in isocyanate groups is reached, the catalyst is destroyed by addition of a deactivating compound selected from among organic compounds (A) bearing at least one hydroxyl group, or the compounds resulting from the reaction of an isocyanate group with said organic compound (A), the organic compounds (A) optionally bearing substituent groups or atoms which are inert towards isocyanate groups, and said compounds including enols, alcohols, phenols, oximes or hydroxysilylated compounds.
The addition of the deactivator, or deactivating compound, is generally performed at a temperature between 50.degree. and 180.degree. C., preferably between 80.degree. and 130.degree. C., and especially at the temperature of cyclotrimerization. Cf. U.S. Pat. No. 3,992,316.
It has now surprisingly been found that the deactivation of the cyclotrimerization catalysts can advantageously be carried out at a temperature below 50.degree. C., in the case where organic compounds bearing at least one hydroxyl group are employed as the deactivator. It has even been established, unexpectedly, that polyisocyanurate/polyisocyanates obtained in this manner show a further improvement in stability relative to those obtained according to the process of French Pat. No. 82/03799. This improved stability is manifested by the inability of the polyisocyanurates obtained by the process of the present invention to generate monomeric diisocyanate during storage, and even during heating for an extended period of time at a temperature greater than or equal to 50.degree. C. It is especially important to avoid the presence of monomeric diisocyanates in polyisocyanurates, which are used in particular for producing coatings, the toxicity of which monomeric diisocyanates being well known.